Placement and detonation method for explosive fracturing

ABSTRACT

A method of oil or gas well stimulation wherein a liquid explosive is injected into the formations and subsequently detonated. An explosive charge is placed proximate the formations containing the liquid explosive and a detonating device is lowered to actuate the explosive charge and liquid explosive.

United States Patent Bullen 1 Sept. 12, 1972 [54] PLACEMENT AND DETONATION METHOD FOR EXPLOSIVE FRACTURING 72 Inventor: Ronald s. Bullen, Calgary, Alberta,

Canada [73] Assignee: Dresser Industries, Inc., Dallas,

Tex.

[22] Filed: Oct. 21, 1970 [21] Appl. No.: 82,668

[52] US Cl ..166/299, 166/63 [51] -Int. Cl. ..E2lb 43/00 [58] Field of Search .166/299, 308, 63; 102/20, 21.6, I 102/86.2

[56] References Cited I UNITED STATES PATENTS 3,066,733 12/ 1962 Brandon ..166/299 2,595,615 5/1952 Sweetman ..102/20 2,928,469 3/1960 Crowe ..l66/l42 X 219,880 9/1879 Sherman ..lO2/2O X 1,406,844 2/ l 922 Gelm lO2/86.2 X 2,246,61 l 6/1941 Zandmer 166/299 2,892,405 6/1959 Chesnut 166/299 3,191,678 6/1965 Hinson 166/299 3,270,8 l 5 9/ l 966 Osborn et al. 1 66/299 Primary Examiner-James A. Leppink Attorney-Robert W. Mayer, Thomas P. Hubbard, Jr., Daniel Rubin, Raymond T. Majesko, Roy L. Van Winkle, William E. Johnston, Jr. and Eddie E. Scott [57] ABSTRACT A method of oil or gas well stimulation wherein a liquid explosive is injected into the formations and subsequently detonated. An explosive charge is placed proximate the formations containing the liquid explosive and a detonating device is lowered to actuate the explosive charge and liquid explosive.

4 Claims, 6 Drawing Figures PNENTED 2 I973 3.690.379

SHEET 1 OF 2 lll l'l g FIG.| FIG 2 INVENTOR RONALD S. BULLE N ATTORNEY PATENTEDSEP 12 I972 FIGLS SHEET 2 or 2 FIG. 6 5 INVENTOR RONALD S. BULLEN ATTORNEY PLACEMENT AND DETONATION METHOD FOR EXPLOSIV E FRACTURING BACKGROUND OF THE INVENTION This invention relates to the art of oil and gas well stimulation and more particularly to a method of detonating a liquid explosive interspersed in the formations.

Huge quantities of hydrocarbons in both liquid and gaseous form exist in underground reservoirs wherein the permeability is too low for production to be economical. Various methods are used to stimulate these formations thereby making production practical. Hydraulic fracturing, acidizing and explosive fracturing are the conventional treatments used. The present invention relates to the latter. Although explosive fracturing is not new, development in this area is currently active and it holds great promise for the future.

The basic theory behind explosive fracturing is relatively simple. Rock is generally less resistant to tension than to compression. The high pressures developed by an explosion shatters the rock [and a shock wave is generated that moves through the formations. The pressures in this shock wave are initially positive but revert to negative values thereby producing the desired fracturing of the formation rock.

' DESCRIPTION OF THE PRIOR ART In U.S.-Pat. No. 3,151,679 to J. Karpovich et al. titled Method, of Fracturing an Earth Formation with a Frangible Implodable Device patented Oct. 6, 1964, the compressional weaknesses of the formations are exploited. A vessel that will implode when exposed to a predetermined pressure range is lowered into a well bore. Liquid is injected into the formation to increase the pressure thereby causing the vessel to shatter and creating a shock wave that travels through the formations.

Nuclear devices have been used in explosive fracturing. On Dec. 10, 1967, a 26 kiloton device was detonated in San Juan Basin, New Mexico under Project Gasbuggy and on Sept. 10, 1969, a 40 kiloton device was detonated at Grand Junction, Colorado under the Rulison Project. These two projects have established the feasibility of using nuclear explosive in oil and gas well stimulation but economic consideration and the practicability of this type of stimulation inject a certain amount of doubt about its future.

Most explosive fracturing of the prior art has consisted of the explosive being detonated in the well bore itself. A more promising explosive fracturing method is the displaced explosive method wherein a liquid explosive is forced into the formations prior to detonation. The fractures created by this method are of an improved configuration thereby producing greater yield.

various operations are completed thus creating a hazard both to personnel and equipment. In addition,

there is no provision for recovery of the time bomb in case of misfire. The electrical cable includes these disadvantages and complicates all additional operations.

SUMMARY OF THE INVENTION The present invention provides an improved system of oil and gas well stimulation. A liquid explosive is positioned to produce fracturing in the formations surrounding a well bore. The various associated rig and well operations are performed. A detonator is then positioned in the borehole and the liquid explosive detonated. I

In one embodiment a charge tube is positioned in the well bore above the formations to be fractured. A detonating element including a shaped charge is then lowered to actuate the liquid explosive through the charge tube. If the system misfires, one or more of the elements may be retrieved and the sequence started again.

It is therefore an object of the present invention to provide safety and economy in the detonation of an explosive fracturing device.

It is a further object of the present invention to provide an explosive fracturing system wherein the detonator is not placed in the well until all pumping and service rig operations are complete.

It is a still further object of the present invention to provide explosive fracturing detonation from above a packer and wiper plug.

It is a still further object of the present invention to provide a system of detonating an explosive fracturing liquid wherein one or more elements of the system may be retrieved in case of misfire.

It is a still further object of the present invention to provide an explosive fracturing system wherein the correct amount of explosive may be positioned in the formations to be fractured.

The above and other objects and advantages of the present invention will become apparent from a consideration of the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the liquid explosive being displaced in the formations.

FIG. 2 shows the detonator in place in the well bore prior to detonation.

FIG. 3 shows a drillable packer including a one-way valve, positioned in the well bore above the formation to be treated.

FIG. 4 shows the explosive liquid being positioned in the formation.

FIG. 5 shows the charge tube in place.

FIG. 6 shows the detonator in position in the well bore prior to detonation.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1, a well bore 10 penetrates a portion of the earths surface including formation 11. A packer 12 has been positioned in the well bore above the formation 11. Liquid explosive 13 has been injected into the well bore and is dispersed into he formations through fractures therein. A one-way valve 14 insures that fluid will not pass upward through central passage in packer 12. A wiper plug 16 and charge tube 17 are moved downward in the well bore 10. The wiper plug 16 insures that all of the liquid explosive 13 will be properly positioned prior to detonation. The charge tube 17 is filled with an explosive such as compacted dynamite. Attached to the upper end of charge tube 17 is a fish neck 18 to allow the wiper plug and charge tube to be retrieved if desired.

As shown in FIG. 2, the charge tube 17 has been lowered into opening 15 through the packer 12. The charge tube 17 may be firmly attached to packer 12. A detonating device 19 is positioned in the well bore 10 immediately above charge tube 17. Included in detonator 19 is .a shaped charge 20. The detonator 19 may be actuated by a conventional actuating device 21.

';Referring now to FIG. 3 another embodiment of the present invention is shown. A portion of a borehole 22 penetrates an earth formation 23. A plug 24 is positioned in borehole 22 below the point wherein fracturing is desired. Casing 25 is perforated thereby producing perforations 26 to allow the liquid explosive to be positioned in the formations. The formations 23 are hydraulically fractured to develop cracks in the formation of maximum width to accommodate injection of the liquid explosive. An injectivity test may than be run to assure the feasibility of the liquid explosive displacement. A packer 27 is placed in the borehole 22 above perforations 26. Packer 27 includes a central passage way '28 and a one-way flapper valve 29 that prevents fluid in the borehole from moving upward. The portion of the borehole above packer 27 is completely swabbed dry tothe packer depth. The one-way valve 29 on packer 27 will hold back reservoir pressure.

Liquid explosive 30 is injected into borehole 22 as shown in FIG. 4. A wiper plug 31 and charge tube 32 are positioned in the borehole 22. The wiper plug 31 may be a flexible cement plug with a center of tubing threaded on both ends. A latch stinger 33 is attached to the charge tube 32 to allow the charge tube to be firmly latched to packer 27. Positioned below the latch stinger 33 is aseal nipple 34 to insure a tight seal between charge tube 32 and packer 27. A bull plug 35 is connected to the bottom of charge tube 32. Charge tube 32 is filled with an explosive such as compacted dynamite. Connected to the top of charge tube 32 is a fish neck 36 to allow the charge tube and wiper plug to be retrieved if desired.

Referring now to FIG. 5, the wiper plug 31 and charge tube 32 have been displaced into packer 27 using water. The latch stinger 33 insures that charge tube 32 is locked into packer 27 thereby fixing the correct explosive placement.

Referring now to FIG. 6, a detonator 37 has been allowed to float down through the water to the top of charge tube 32. The detonator 37 includes a large shaped charge 38 facing downward. An actuating mechanism 39 is positioned to actuate shaped charge 38. A centralizing tube 40 insures proper orientation of the detonator. Attached to the upperend of detonator 37 is a fish neck 41 to allow the detonator to be retrieved in case of misfire.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of stimulating formations surrounding an earth borehole by the use of a liquid explosive, comprising the steps of:

positioning a packer in the earth borehole above the formations to be stimulated, said packer having an opening therethrough;

injecting a liquid explosive through said opening in said packer into the formations;

positioning an explosive charge in said opening in said packer so that said explosive charge extends through said opening and is proximate the formations containing the liquid explosive, and

lowering a detonator to activate the explosive charge.

2. A method of stimulating the formations surrounding a well bore by the use of a liquid explosive, comprising the steps of:

hydraulically fracturing the formations to develop cracks therein;

installing a packer with a central opening and a oneway valve in said central opening above the formations to be stimulated;

injecting a liquid explosive into the well bore through the central opening in said packer and the one-way valve in said central opening and into the cracks in said formation;

installing an explosive charge through the central opening in said packer so that said explosive charge is proximate the formations containing the liquid explosive; and

lowering a detonator to explode said explosive charge and liquid explosive.

3. A method of stimulating the formations surrounding a well bore by the use of a liquid explosive, said well bore being cased by a suitable casing, comprising:

installing a plug in said casing below the formations to be stimulated;

perforating the casing in the area of said formations to be stimulated;

hydraulically fracturing the formations to develop cracks therein;

installing a packer above the formations to be stimulated, said packer including a central opening and a one-way valve in said central opening;

injecting a liquid explosive into the well bore through the central opening in said packer and into the cracks in said formations;

cleaning the well bore above said packer; and

installng an explosive charge through the central opening in said packer so that said explosive charge is proximate the formations containing the liquid explosive; and lowering a detonator to explode said explosive charge and liquid explosive.

4. Apparatus for stimulating formations surrounding an earth borehole, comprising:

a packer that may be positioned in said borehole, said packer including a passage that allows fluid to pass through said packer;

means for preventing fluid from passing upward through said passage in said packer;

a charge tube including an elongated portion that is adapted to be positioned in said passage, said charge tube including an explosive and means for allowing said charge tube to be retrieved; and

means for detonating said explosive, said means for detonating said explosive including a shaped charge positioned in a housing adapted to be lowered into said well bore and a fish neck connected to said housing for allowing said housing 5 and shaped charge to be retrieved. 

2. A method of stimulating the formations surrounding a well bore by the use of a liquid explosive, comprising the steps of: hydraulically fracturing the formations to develop cracks therein; installing a packer with a central opening and a one-way valve in said central opening above the formations to be stimulated; injecting a liquid explosive into the well bore through the central opening in said packer and the one-way valve in said central opening and into the cracks in said formation; installing an explosive charge through the central opening in said packer so that said explosive charge is proximate the formations containing the liquid explosive; and lowering a detonator to explode said explosive charge and liquid explosive.
 3. A method of stimulating the formations surrounding a well bore by the use of a liquid explosive, said well bore being cased by a suitable casing, comprising: installing a plug in said casing below the formations to be stimulated; perforating the casing in the area of said formations to be stimulated; hydraulically fracturing the formations to develop cracks therein; installing a packer above the formations to be stimulated, said packer including a central opening and a one-way valve in said central opening; injecting a liquid explosive into the well bore through the central opening in said packer and into the cracks in said formations; cleaning the well bore above said packer; and installng an explosive charge through the central opening in said packer so that said explosive charge is proximate the formations containing the liquid explosive; and lowering a detonator to explode said explosive charge and liquid explosive.
 4. Apparatus for stimulating formations surrounding an earth borehole, comprising: a packer that may be positioned in said borehole, said packer including a passage that allows fluid to pass through said packer; means for preventing fluid from passing upward through said passage in said packer; a charge tube including an elongated portion that is adapted to be positioned in said passage, said charge tube including an explosive and means for allowing said charge tube to be retrieved; and means for detonating said explosive, said means for detonating said explosive including a shaped charge positioned in a housing adapted to be lowered into said well bore and a fish neck connected to said housing for allowing said housing and shaped charge to be retrieved. 